This invention relates to gas lasers, and particularly gas lasers using a gas discharge in a waveguide as the laser medium.
A gas laser is operated by creating a discharge in a gas within an optical resonator. The discharge causes an overpopulation of upper energy levels within the gas, and the subsequent transition to lower energy levels releases light at discrete frequencies within the resonator to maintain lasing action. In a typical gas laser, a hollow tube confines the discharge between the mirrors of the optical resonator.
Portable gas laser systems require small rugged lasers having large specific power, namely high power per laser mass or laser volume. An important step in increasing the specific power of continuous wave gas lasers was the development of a waveguide gas laser that works in discharge tubes with circular or rectangular cross sections on the order of one square millimeter. However, several factors limit the specific power of such lasers. The power per discharge tube length is limited and does not significantly differ from conventional large bore lasers. Also, the top and side walls of the waveguide, and the optical resonator at the ends, limits the opportunities for cooling the laser.
An article in Lasers and Optronics, May 1988, pages 19 and 20, describes a laser system in which a two-dimensional waveguide confines the discharge. Here, the author generates a multiplicity of parallel discharges within a rectangular cavity with a series of cathodes along one edge of the waveguide and a series of anodes along the other. The author states that if the cavity were merely filled with a laser gas mixture, a DC discharge would not uniformly fill the cavity. It would "neck down" to several discrete discharge channels. A constant magnetic field applied perpendicular to the plane of the cavity would force the discrete discharges to sweep through the cavity and deplete electrons from one end of the cavity and cause termination of the discharge at the other end. To overcome this disadvantage, a "launcher" in the form of an extended anode that lies on the surface of the cavity increases the electric field strength in the area of the cavity that must continuously initiate new electrical charges. These new electrical charges offset the magnetic forces that sweep the discharges through the cavity. With sufficient magnetic field strength, a transition occurs from discrete moving discharges to a homogeneous and uniform discharge. Laser action occurs during this homogeneous and uniform discharge.
However, operation of such a waveguide laser depends upon several factors, including gas pressure, current density, and electrode configuration to obtain the required homogeneity. This creates a cumbersome interrelationship of operational factors which limit the applicability of this device.